May, 1932
CARBON TETRABROMIDE AS A BROMINATING AGENT
2025
summary 1. Under the conditions used by us sodium ethylate is not a useful reagent for obtaining the sodium salt of phenylacetonitrile. 2. A considerable quantity of sodium phenylacetonitrile is undoubtedly formed in the reaction of the nitrile with sodium ethylate but much of the salt condenses with the mononitrile to form a dinitrile. 3. a-Phenylbutyronitrile was not found to condense with itself under the influence of sodium ethylate in ether. 4. The syntheses of the chloride and amide of a-phenylbutyric acid are reported. CHICAGO, ILLINOIS [CONTRIBUTION FROM
TEE SCHOOL O F
CHEMISTRY O F
THE
UNIVERSITY OF MINNESOTA]
CARBON TETRABROMIDE AS A BROMINATING AGENT1 BY W. H. HUNTER AND D. E. EDGAR RECEIVED JANUARY 2, 1932
PUBLISHED MAY7, 1932
During the study of certain reactions of carbon tetrabromide and aniline in xylene solution, it was observed that the xylene was brominated. Accordingly, an investigation was started with the point of view of dctermining the possible use of carbon tetrabromide as a brominating agent. In the case of the majority of compounds studied, bromination with this reagent took place, and when this occurred bromoform was always a byproduct. Most of the bromo compounds prepared in this work can be made more easily by other methods, so that, as a rule, the use of carbon tetrabromide does not have any advantages over the commoner methods, but our experiments indicate that there are certain regularities with brominations using carbon tetrabromide that may be very useful, and the most important of these is the preferential side chain bromination of alkylbenzenes.
Experimental Part Preparation of Carbon Tetrabromide.-The method of Wallachl served as a basis for our modified preparation of carbon tetrabromide from acetone and sodium hypobromite. The preparation as described is suitable for the production of large quantities of carbon tetrabromide in good yield. Since bromoform is a by-product in all cases of brominations described here, use was also made of a method similar to Habermam’s,* involving bromoform and aqueous sodium hypobromite. Although Habermann stated that direct light was necessary, it was found that as good a yield of carbon tetrabromide could be obtained in the complete absence of light. The work described in this paper constituted part of a thesis submitted to the graduate faculty of the University of Minnesota by Donald E. Edgar in partial fulfilment of the requirements for the degree of Doctor of Philosophy, May, 1927. This paper was prepared by the junior author after the death of Dr. Hunter.- [L. I. SYITH.] * Wallach, Ann., 275,149 (1893). * Habermann, ibid., 167,174 (1873).
2026
VOl. 54
W. H. HUNTER AND D. E. EDGAR
( a ) From Acetone.-A four-liter container (fitted with a mechanical agitator) was approximately half-filled with shaved ice. To this was added 2500 cc. of sodium hydroxide solution containing 150 g. of sodium hydroxide to the liter; 200 cc. of bromine was added rapidly with stirring. Then 60 cc. of acetone was added in small portions (5-10 cc.), time being allowed after each addition for the milky precipitate formed (probably bromoform) to be converted into lumps of carbon tetrabromide. After addition of this amount of acetone, 1-cc. portions were added cautiously until the characteristic yellow hypobromite color had been discharged. The crude carbon tetrabromide was separated by filtration and purified by crystallization from alcohol. (b) From Bromoform.-A sodium hypobromite solution was prepared as in (a) but with only one-fourth of the amounts of materials. This is sufficient to convert 150 g. of bromoform to carbon tetrabromide. All of the bromoform was added a t one time and the mixture was shaken or stirred vigorously. Procedure in Bromination Experiments.-The reactions were carried out by heating carbon tetrabromide with various materials in sealed tubes, in the proportions of 1:l unless otherwise noted. The temperature, in general, was 150-BO", and the time of heating about eight hours. In practically all cases, separation and purification of resulting products was accomplished by fractional distillation under diminished pressure. Identification of the products was by analysis for bromine, together with physical properties. The method of analysis was that of Stepanoff, as modified by Drogin and Rosanoff,' which was found to be rapid and convenient.
TABLE I RESULTSOF EXPERIMENTS IN WHICHALIPHATIC COMPOUNDS WERE THE REACTANTS WITH CARBON TETRABROMIDE Yield, %
Reactants with CBrr
Product
%-Heptane Acetic acid Propionic acid Sym.-tetrabromoethane
Decomposition Bromoacetic acid a-and P-monobromopropionic acids (mixture) Pentabromoethane Hexabromoethane Hexabromoethane
Pentabromoethane
.. 32.4 42.2 10.1 2 Trace
TABLE I1 RESULTS WITH AROMATIC COMPOUNDS Reactants with CBrr
Yield, % '
Product
67.6 Benzene Bromobenzene 76.9 Toluene Benzyl bromide Ethylbenzene 1-Phenyl-1-bromoethane 66.6 70.3 Ethylbenzene" 1 -Phenyl-1,2-dibromoethane 46.7 1-Phenyl- 1-bromopropane 72- Prop ylbenzene .. Cumene Decomposition 67.3 m-Xylene m-Xylyl monobromide 48.4 m-Xylenea m-Xylylene dibromide 33.5 DuryI monobromide Durene 100 Dureneb Addition product, 1 : l 74.5 Naphthalene a-Bromonaphthalene Room temperature in a Two moles of carbon tetrabromide to one of reactant. carbon disulfide solution.
'
Drogin and Rosanoff, THIS JOURNAL, 38,711 (1916).
May, 1933
CARBON TETRABROMIDE AS A BROMINATING AGENT
2027
I n the study of aromatic hydrocarbons, described above in Table IT, several interesting facts were noted. Bromination, by this method, takes place preferentially in the side chain rather than in the ring: the first point of attack being, in these cases, the alpha carbon of the chain. The decomposition of isopropylbenzene, whereas n-propylbenzene is brominated, suggests a method of differentiating between normal and is0 linkages to the ring. Duryl Monobromide (CloHlsBr).-This compound, which has not heretofore been prepared, resulted from the reaction of carbon tetrabromide and durene in the general manner described above and in Table 11. Duryl monobromide is a clear, practically colorless liquid boiling a t 110-112° under a pressure of 4 mm. It has a not unpleasant odor, somewhat resembling that of benzyl bromide, but is free from lachrymatory action. With alcoholic silver nitrate it gives an immediate precipitate of silver chloride, while monobromodurene, a solid having a melting point of 61 "'-the only other monobromo derivative of durene-gives no precipitate. Anal. Calcd. for CIOHIIBr: Br, 37.51. Found: (Stepanoff) Br, 37.78, 37.69; (Carius) Br, 37 88,37.82; (alc. AgNOa) Br, 37.81, 37.86. Durene-Carbon Tetrabromide Addition Product (CloH1cCBrJ.S-Durene and carbon tetrabromide were dissolved in equivalent molecular proportions in an excess of carbon disulfide. The solution was allowed to stand a t room temperature until the carbon disulfide had evaporated. The material remaining was in the form of large, welldefined crystals different in form from those of durene or of carbon tetrabromide, m. p. 84-86". Mixed melting points of this material with either durene or carbon tetrabromide gave a lowering of the melting point. Anal. Calcd. for C I O H ~ I C BBr, ~ ~ :68.62. Found: Br, 68.29, 68.51.
TABLEI11 REACTIONS WITH AROMATIC COMPOUNDS Reactants with C B n
Product
Yield,
%
Bromobenzene p-Dibromobenzene Benzyl bromide
p-Dibromobenzene 42.5 No reaction .. Benzal bromide 55.3 Benzal bromide 74.5d Benzyl bromide" Benzotribromide 21.4 Benzal bromide Benzotribromide 27.2 Phenol' (Aurin) .. AnilineC (Pararosaniline) .. Nitrobenzene, m-dinitro benzene, and benzoic acid gave no reaction, even on prolonged heating, while hydroquinone was completely decomposed. " Two moles of carbon tetrabromide to one of reactant. * One mole of carbon tetrabromide to ten of reactant; refluxed for thirty minutes. ' One mole of carbon tetrabromide to thirteen of reactant; refluxed for one hour. d Temperature, 210". Table I11 records the reactions of various aromatic compounds. It is interesting to note that bromination did not take place with any of the compounds having a meta orienting group already present. Phenol and carbon tetrabromide when heated together a t atmospheric pressure gave a bright red material which was not studied further a t this time. It was perhaps aurin, since Gomberg and Snow6 have described the formation of this dye from phenol and carbon tetrachloride. Likewise, in the case of aniline, paras We wish to express our thanks to Dr. L. I. Smith for his generosity in providing the durene and bromodurene which made possible these experiments. Gomberg and Snow, THIS JOVRNAL, 47,198 (1925).
2028
VOl. 54
EDWIN C. KNOWLES AND JOHN B . CLOgE
rosaniline was perhaps the product since Hofmann’ obtained it similarly by the action of carbon tetrachloride. It will be noted in Table 111that benzotribromide was the product of two reactions. This compound is described here for the f i s t time, as far as the writers are aware. A search of the literature revealed only one mention8 of this compound and that was in a statement to the effect that benzotrichloride (or bromide) is readily hydrolyzed by water or potassium hydroxide to benzoic acid. It was found that several hours of heating with 10% sodium hydroxide was required to bring about hydrolysis of a 3-g. sample. Benzotribromide (C;HsBr&-Benzotribromide resulted from the reaction of two equivalents of carbon tetrabromide with one of benzyl bromide and also from one equivalent of carbon tetrabromide with one of benzal bromide. Hydrolysis of the product resulted in the formation of benzoic acid. Benzotribromide is a colorless crystalline material, very soluble in alcohol or ether, less soluble in petroleum ether, insoluble in water: m. p. 56-57’, Anal. Calcd.: Br, 72.91. Found: Br, 72.76, 72.61 (Stepanoff); 72.85 (alc. AgNOs).
Summary 1. Carbon tetrabromide will react with various organic materials through the exchange of a bromine atom for a hydrogen. Bromoform is always the by-product of such bromination. 2 . Carbon tetrabromide brominates selectively the side chains of the benzene hydrocarbons instead of attacking the ring. 3. Duryl monobromide, benzotribromide, and an addition product of durene and carbon tetrabromide are described. 7
Hofmann, J . prakt. Cltem., 77,191 (1859); 87,226 (1862).
* Fry,THISJOURNAL,36, 1043 (1914). MINNEAPOLIS, MINNESOTA [CONTRIBUTION FROM
THE
WALKERCHEMICALLABORATORY OF
THE
RENSSELAER
POLYTECHNIC INSTITUTE]
SUBSTITUTED PHENYLACETONITRILES AND DERIVATIVES. 1-PHENYL-1-CYANOCYCLOPROPANE, ALPHA-PHENYLGAMMA-HYDROXYBUTYRONITRILE,ALPHA-PHENYL-GAMMACHLOROBUTYRONITRILE AND ALPHAPHENYLCROTONONITRILEI BY EDWINc. KNOWLESAND RECEIVED JANUARY 2, 1932
JOHN
B. CLOKE
PUBLISHED MAY7, 1932
In the development of a series of investigations on sundry cyclic ketimines, imino esters and heterocyclic nitrogen compounds, supplies of a-alkyl and a-aryl-7-chlorobutyronitrilesand alkyl and aryl substituted cyclopropyl cyanides were required. The present paper describes the preparation of one of the chloro and two of the cyclic compounds. 1 This paper is from the first part of a thesis presented by Edwin Chandler Knowles in June, 1931, to the Graduate School of the Rensselaer Polytechnic Institute in partial fulfilment of the requirements for the degree of Doctor of Philosophy.
